1. Field of the Invention
The present invention relates to an improvement in the display characteristic of an eyepiece image display apparatus which can be held at a user's head or face.
2. Description of the Related Art
In recent years, for the purpose of "virtual reality" or personally enjoying a large-screen image, visual display apparatuses of a helmet type or goggle type which are held at a user's head or face have been developed. For example, one of them enlarges an image on a small display element such as a liquid display element, an EL display element, etc., and projects it onto an eyeball through an eyepiece optical system such as a lens. The optical system for such an eyepiece visual display apparatus is shown in FIG. 6.
In FIG. 6, reference numeral 1a, 1b denotes a two-dimensional display element, respectively; 2a, 2b denotes an eyepiece lens for enlarging and projecting it in the air; and 3a, 3b denotes an eyeball of an observer 3. In a conventional device, the enlarged virtual image of an original image formed on the two-dimensional display device 1a, 1b is formed by the eyepiece lens 2a, 2b and seen as an enlarged virtual image by the eyeball 3a, 3b.
For a head/face fitting visual display apparatus, assuring a large view angle is required to enhance the presence of a screen. It is not too much to say that the presence is critically dependent on the view angle provided. Realization of an eyepiece optical system permitting the image display over a wide angle is required to give the presence of a three-dimensional effect, intensity, immersing sense, etc. to an observer.
Where an enlarged virtual image is formed by the two dimensional display device arranged in the neighborhood of a refractive optical system having positive power or a reflective optical system/reflective-refractive composite optical system which is used as an eyepiece optical system, optical designing is made so as to arrange an incident pupil (aperture stop) at the position of an eyeball of an observer to correct several kinds of aberrations. Where such a wide-angle enlarged optical system is designed, since the aperture stop is located before the optical system, positive distortion aberration is generated inevitably in the enlarged virtual image formed by the optical system.
FIG. 7 is a graph showing the result of computation of the distortion aberration when an enlarged virtual image is formed at a position of 3 m in front of an eyeball using an eyepiece lens according to the tenth embodiment in Japanese Patent Application No. Hei 9-54970 hereby incorporated by reference. In this graph, it is assumed that a two-dimensional display element has an effective display area of (horizontal 26.88 mm.times.vertical 20.16 mm, diagonal 33.6 mm), and the center of the two dimensional display element is located at that of an optical axis. In this example, it can be seen from FIG. 7 that a large distortion aberration of 55% is produced at a diagonal end.
FIG. 8 is a view showing the simulation result of a display image based on a positive distortion aberration. Ip denotes the display state of grid lines which divide an effective display area having an aspect ratio of 4:3 into 8.times.6 square regions. Fp denotes the contour of the region of the effective display image when there is no distortion. It can be understood how appreciation of a natural wide angle image is obstructed because an enlarged distorted image of a spool shape is displayed.
FIG. 9 is a graph showing a magnification color aberration in a state where a virtual image has been formed in the same eyepiece lens system described above. This illustrates the computation result of long wavelength light (610 nm : red) and short wavelength light (470 nm : blue). It can be seen from the figure that large color aberration (red is smaller than blue) exceeding 30 mm is generated at a diagonal end so that where an original image is constituted by an arrangement of three primary colors of red, blue and green, deterioration of the resolution of the display image due to the shear of three primary color image as well as spool-shaped distortion occurs.
The present invention has been accomplished in order to solve the above problem. The first problem is to provide an eyepiece image display apparatus for enlarging/displaying an image formed on a two-dimensional display element, which can correct the distortion in an eyepiece optical system by electrically creating an inverse-distorted image.
The second object of the present invention is to provide an eyepiece image display apparatus which can correct magnification color aberration as well as distortion aberration in an eyepiece optical system.
In order to solve the above problems, the eyepiece image display apparatus comprises a two-dimensional display element; a signal processing circuit for processing an image signal to be displayed on the two-dimensional display element; an eyepiece optical system for enlarging and projecting the image displayed on the two-dimensional display element as a virtual image on a human's eyeball, where the signal processing circuit includes an inverse-distorted image creating means for creating an inverse-distorted image attenuating distortion aberration in the eyepiece optical system on the two-dimensional display element.
The inverse-distorted image created by the inverse-distorted image creating means is a barrel-shaped distorted image displayed on a smaller region than the display region of the two-dimensional display element.
The inverse-distorted image created by the inverse-distorted image creating means is a barrel-shaped distorted image which has a size in a horizontal direction which is equal to that of the display region in the horizontal direction of the two-dimensional display element.
The inverse-distorted image created by the inverse-distorted image creating means is a barrel-shaped distorted image which has a size in a vertical direction which is equal to that of the display region in the vertical direction of the two-dimensional display element.
The inverse-distorted image created by the inverse-distorted image creating means is a barrel-shaped distorted image which has a size in a diagonal direction which is equal to that of the display region in the diagonal direction of the two-dimensional display element.
The image displayed on the two-dimensional display element is composed of three primary components of red, green and blue, and the inverse-distorted image created by the inverse-distorted image creating means is subjected to inverse-distortion correction for each of the three primary colors so that magnification color aberration of the eyepiece optical system is also attenuated.
The two-dimensional display element, eyepiece optical system and signal processing circuit are provided in duality, respectively so as to correspond to left and right eyeballs of an observer.
The inverse-distorted image creating means serves to display a black image in a portion outside the inverse-distorted image and within the effective display-region frame of the two-dimensional display element.